Example 4.1.6. This example illustrates the elimination of useless symbols using the algorithms from the proofs of Theorems 4.1.2 and 4.1.3.
S _ bb | aB
A _ a | Aa
B _ bB | Ba | AB
C _ ba | aA | Bb | aCb.
First V0 = {S, A, C} = V1 = V' so B is dead and all red productions can be removed.
Then R0 = {S}, R1 = {S, b} = R2 so a, A, and C are unreachable and all violet productions can be removed.
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